In search of a better bee

Unaffected by Varroa, tolerant of cold and able to pollinate in enclosed spaces, bumblebees offer new hope for New Zealand’s primary industries. If only we knew how to build a nest they wanted to live in…

This year, pollination scientist David Pattemore is adding to his repertoire of skills: he is learning how to train a puppy to hunt dumbledores. Or, if you’d prefer modern English, bumblebees. He hopes that one day his Hungarian Vizsla will sniff out their nests.

It’s a branch of Pattemore’s day job at Plant & Food Research. He heads a project trying to coerce wild bumblebees to take up residence in orchards and on pasture, where they are wanted to help out with pollination. This vital job, which is traditionally done by honeybees, keeps our bellies full and our horticultural industry afloat. Most of our fruit and vegetable intake relies on successful crop pollination.

Honeybees are getting pricey, however. Varroa has hiked costs. But another, sweeter factor has crept into the equation: manuka honey is known as the most expensive type in the world, with prices roughly doubling over the past five years. Our other honeys have grown more expensive in its wake.

David Pattemore with his five- month-old Vizsla, Ollie, being trained to sniff out bumblebee nest wax. By locating early- stage nests, Ollie will help scientists design nest boxes to lure bumblebees into orchards and pastures.

The increased price of pollination by honeybees is linked to the price of manuka honey, says Federated Farmers bee industry group chairman John Hartnell. “The reality is that beekeepers get more money by putting hives into manuka than putting them into pollination. The other side issue with pollen from kiwifruit and some other crops is that the pollen is lower in protein, so it’s not attractive for honeybees. They have to work a lot harder, and come out in not as good a condition as they go in.”

Bumblebees are an appealing alternative, and not just because they are unaffected by Varroa. A bumblebee worker is said to do the kiwifruit pollination work of 50 honeybee workers, with its furry body described as a powder puff compared to the cotton bud that is a honeybee. It’s also a more intrepid worker, flying in the cold, wind and rain, when honeybees stay snuggled up in the hive. Such weather conditions are typical of spring in New Zealand, the crucial pollination season.

Growers of commercial glasshouse crops, particularly tomatoes, have long relied on bumblebees. Bumbles are happy to forage close to home, whereas honeybees wander more widely and object to being trapped in a glasshouse.

Tomato flowers benefit hugely from the bumbles’ special talent, buzz pollination. The bee grabs a flower in its mandibles and violently buzzes. The shaking causes pollen to drop onto the bee, coating the female parts of the flower as it falls.

The solution for glasshouse growers is to buy ready-made commercially produced bumblebee hives, which are reared indoors and arrive by courier in a cardboard box. The bees do a better job than people hand pollinating, boosting tomato size and flavour and upping the yield by around 20 per cent.

The queen bumblebee can be more than twice as large as a worker. An established bumblebee nest looks like a ramshackle waxen slum, housing as many as 300 bees. The nest cells, built to house larvae and then recycled as nectar pots, are piled on top of each other like a wobbly stack of igloos.

It’s enough to turn an Australian tomato grower green: over there, only Tasmania has bumblebees, due to concerns that bumbles would pollinate weeds and outcompete native pollinators. Mainland tomato growers instead buzz each flower by hand with a vibrating wand.

Luring wild bumblebees to artificial nest boxes should be a cheap alternative, yet it’s proved so unsuccessful that groups in other countries have all but given up.

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The need for inexpensive, reliable pollination is such that Pattemore’s project has been awarded several million dollars of government and grower funding over six years.

The research team has plenty on its ‘to-do’ list. Because bumbles give no reward in the form of a honey stock, humans have never figured out how to manage them the way we do honeybees. Bumblebees make only enough honey to sustain their colony through to autumn, when they die. Only young queens survive, hibernating underground over winter.

It is the newly emerged queen that the scientists particularly seek to understand. For once she has recharged herself with nectar, it is her mission to choose a nest site and establish a colony.

The researchers want her to nest in their experimental orchards and pastures, and they are trying to entice her with pre-made nest boxes.

To do so, they need to find out just what constitutes queen-friendly real estate, be it the shadiness of the nest tunnel entrance, the landscape features outside it, or the nesting material inside.

“Our challenge is to come up with a ‘bumblebee bunker’ design that works for growers, is practical and can be scaled up,” says Pattemore. “Growers need to be able to lift the lid and know how many successful bumblebee nests they have, so they can figure out how many honeybee hives they need to order.

“We’re not trying to replace honeybees. They will always be the cornerstone pollinators globally. But relying on a single species of pollinator is not a good idea, and bumblebees are likely to be an excellent second option.”

So far the researchers have found that the most popular nesting material is Pink Batts nestled in a cube walled in by a breathable concoction of pumice, sand and cement. The cube is buried in the ground, and a plastic pipe leads from underneath it up to ground level, forming an entrance tunnel for the bees.

“We have placed over 900 bunkers in 31 orchards and pasture sites spread throughout five regions, from Whangarei to Marlborough,” explains Pattemore. The sites cover the spectrum of the industries co-funding the project: red clover seed fields, and avocado, stone fruit and kiwifruit orchards.

The kiwifruit industry is particularly interested in the bumbles’ ability to cope with covered crops. Gold fruit orchards are increasingly being covered to protect against wind damage that exposes them to the
devastating kiwifruit pathogen Psa, says Zespri’s Shane Max.

The growers take part in citizen science trials, reporting monthly on how many bunkers are occupied and how many of them go on to form colonies.

On an international scale, the team’s success at luring queens to the bunkers is outstanding—around 30 per cent on average, compared to three per cent overseas. The New Zealand sites have ranged from 0 per cent to 70 per cent occupancy.

The researchers know that fluffy nesting material is vital, and have found that house insulation is chosen by the queens more often than hay or the remains of mouse nests. Queens don’t collect nesting material, but arrange what they find in nest cavities into a cosy tennis-ball sized orb. In nature, the fluff may be animal fur from an old rodent nest, or dried plant material.

The royal nest preparations continue from there. Within the warm orb of fluff the queen crafts a thimble-like cup from her own wax, which she fills with nectar to snack on while she incubates. Finally, she fashions a pea-sized ball of pollen she has collected, coating it in wax as a finishing touch.

Waikato University student Ashleigh Weatherall deftly wields a scalpel at Plant & Food Research’s Ruakura campus to shave a patch of fur so that a radio transmitter can be glued onto a bumblebee queen’s abdomen. She holds the queen steady between cotton wool and netting at the end of a modified syringe. Unharmed by the process, the queens are later released. Bumblebees have a gentle nature in most situations—Weatherall has never been stung—but, when angered, they can sting repeatedly, much like a wasp.

Thus prepared, she lays her eggs, fertilised by sperm stored from her mating tryst the previous autumn. These she places inside the pollen ball, which will become her offspring’s first food. She then crouches over the ball and incubates it like a clucky hen, shivering to keep it warm.

Shivering burns much energy, and the nectar is not enough. At times she must leave to seek more. If there are not enough flowers nearby to fuel the queen, the eggs die and the nest fails.

“Vastly more queens go through this process than succeed; most die trying,” says Pattemore.

Like all bees, bumblebees feed exclusively on nectar and pollen. A shortage of flowers is often cited as the primary challenge faced by insect pollinators around the world. This is particularly likely to be the case in places like kiwifruit orchards, says bumblebee specialist Nelson Pomeroy, where a monoculture of vines is broken only by shelterbelts. The science team plans to look at growing flowers around orchards to sustain the bees before and after the brief glut of crop flowers.

Pomeroy holds the unofficial world record for luring bumblebees to artificial nests—a 93 per cent occupancy rate—which he achieved in Taranaki in the 1970s. The Plant & Food bunker design is based on his findings.

Having any success at all with artificial nesting boxes makes New Zealand a little bit famous among the world’s bumblebee fraternity. Elsewhere, the results have been dismal, so there has been no other serious attempt to formally enlist wild bumbles for pollination.

Even the impressive occupancy achieved by the Plant & Food team could be slightly better. The snag lies with the bees’ tongues, all of which are longer than honeybee tongues, and some are longer than others.

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New Zealand has four species of bumblebee. By far the most common is the short-tongued, white-bottomed large earth bumblebee, Bombus terrestris. It was another species—Bombus ruderatus, a rarer long-tongued, deep-dipping red clover feeder—that Pomeroy had so much success with in the 1970s, and this has also been best at occupying the bunkers of Pattemore’s team. B. ruderatus happily pollinates orchard flowers, but the short-tongued B. terrestris species would be a better catch.

“Because there are so many more terrestris than ruderatus queens—around 40 to 1—if we got just 10 per cent of them establishing colonies in the bunkers we’d revolutionise pollination in New Zealand, and probably elsewhere,” says Pattemore.

The long-tongued queens appreciate the real estate, but the design needs tweaking for the more numerous but apparently fussier short-tongues.

One avenue the researchers are exploring is forced tenancy. Pomeroy has been breeding small short-tongued “starter” colonies for experimental bunkers on Hawke’s Bay orchards, with most of them successfully establishing for the summer.

The team are also working to discover the picky queens’ preferences by studying their wild nests. Tracking down nests in their earliest stages is hard. It is easier when a colony is established, but by then aspects of it will have changed; key plants may have stopped flowering, for example.

The challenge will hopefully be no match, however, for a certain dog with a fine nose. Bumblebee wax has a distinctive smell, and Pattemore, his family and his team are training young Ollie to find it.

From his tiny puppy days, they have played food-finding games with Ollie, honing his skills as a tracking and hunting dog. They progressed to wax-searching challenges, and at five months old he easily finds containers holding nest wax. He sits to identify them and earn his food prize, moving on from identical empty containers.

The team’s next step is to mimic real early-spring nests by having him find small amounts of wax at the end of underground tunnels. This spring, they hope to take him out on real missions to sniff out nest entrances.

If Ollie succeeds, he will be the world’s first sniffer dog to find bumblebee nests at a stage too early for humans to detect. Other dogs have learnt to find large nests, but none have honed in on queens just beginning to build their brood.

Like other bees, the bumblebees’ large compound eyes cannot see red, but can see ultraviolet light that humans cannot. In addition, three jewel-like ‘primitive eyes’ that detect changes in light intensity can be seen in the hairless patch between the top of the large eyes.f if

Leaving no stone unturned, the team have also tracked short-tongued queens in a more high-tech way: using radio transmitters. These have only recently become available in a tiny 200-milligram size, light enough for a 650- to 900-milligram queen to carry. (Bumblebees can bear their own weight in pollen and nectar.)

The researchers recruited Massey University master of science student Katie Ashley, who upped the number of queens she could radio-track last year by traversing the planet to fit in two spring seasons—in the Netherlands and Manawatu. Collaborating with researchers at the University of Amsterdam, she captured foraging queens and glued radio transmitters on their furry abdomens. She
was then able to track the queens back to their nest entrance.

“When we found a nest, we took a large-scale description, such as whether the nest was in the middle of a field or under pine trees, then we went down a level to describe the ground cover, such as what plants or leaf litter type was present. Finally, we recorded a general soil description, distance from nearest tree, aspect of any slope present, and so on,” says Ashley.

Similar details will be recorded about nests that Ollie sniffs out, with the intention of replicating as many of the geographic and structural features as possible in the design and placement of artificial bunkers.

The radio-tracking results are unpublished as yet, but Ashley has some clues. “Evidence points towards intensive farming and monoculture as a sure way to discourage bumblebees from nesting in an area,” she says. “Habitat variability is key. And queens appear to have a preference for nesting under some sort of cover rather than in an open area like a field.”

Ashley’s Dutch collaborators will apply the results to conservation efforts, which are the focus of most international bumblebee research. Three of the world’s 250 species have already gone extinct, and others are perilously close to doing so.

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Like so much of our wildlife, our bumblebees are a northern hemisphere import, brought here from Britain to pollinate red clover. Red clover is an important animal fodder, but it initially set little seed in New Zealand because it arrived without its ideal pollinator, the bumblebee.

The downside of being cold-hardy is that bumblebees can’t bear the heat,
so the first to be shipped across the equator to service red clover died in the tropics. Kiwi farmers had to keep importing seed until the advent of refrigerated shipping.

In January 1885, a batch of chilled, hibernating queens arrived in Lyttelton on the SS Tongariro. They warmed up, ate some honey, flew away and thrived, unaware that they had just made history as the first-ever insects to be introduced to a country to pollinate a particular flower.

Happily, they left behind most of the bumblebee diseases.

More than a century later, some of their descendants hit world headlines as they became the focus of an international rescue plan. One of the four species brought to New Zealand, the short-haired bumblebee, had subsequently become extinct in the United Kingdom. (It is also our rarest.) The British Bumblebee Conservation Trust began a campaign to repatriate it to Dungeness, Kent, which had been the short-haired’s final stronghold.

A publicity campaign was launched to help recreate the area’s former flower swathes, and was backed by other organisations. Farmers were excited to be involved in bringing back an extinct bee and planted wildflowers aplenty. A windfarm sowed a vast expanse of blooms under its turbines. Hundreds of hectares of flower-rich habitat were created. The floral repatriation scene was set.

Bumblebees were introduced to New Zealand to pollinate red clover flowers such as these. This short- tongued Bombus terrestris queen managed to lap up some nectar, but long-tongued species are better at reaching into red clover’s deep florets to drink the sweet liquid. The tongues of the two long-tongued bumblebee species in New Zealand are nearly as long as their bodies. Sometimes short-tongued bumblebees “cheat” by puncturing a hole in the side of deep florets to gain access.

At the last minute, however, the New Zealand bees were rejected. Genetic testing showed that our bees were “decidedly weird” compared to the United Kingdom museum specimens. They were pronounced extremely in-bred, being descended from probably just two queens. Reluctantly, the Brits instead released a Swedish version of the same species, which had never set foot in Britain until 2012 but was genetically more similar to their lost bee.

The current British passion for bumblebees is also reflected in the United Kingdom’s agri-environment schemes, which provide funding to encourage the re-establishment of hedgerows and wildflowers for pollinators.

Bumblebees may be the only wild furry imported creatures that New Zealanders love; they are a slice of Beatrix Potter that are as helpful on this side of the globe as in their northern homeland. Their charm is almost a problem for Pattemore, who tells his growers in vain not to change their pesticide use.

“The bumblebee programme has to work across the board in conventional and organic orchards,” he says. “So we tell them we don’t care what sprays they use, but we ask them to keep a record of what they’ve used and when. But what we’ve found is that many of them do alter their pesticide use to take account of the bees, because they like
them. The bumblebees themselves are causing growers to consider how and when to best use pesticides.”